VB'Net Multiple Form Apps

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VB.Net Multiple Form Apps

• ITE 285 R.Johnson

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A Single Form Project

• By default, project starts from Form1. In menu
  see ProjectgtProperties, Startup Object.
• Form1, what is created in the Form Designer, is
  actually defining a class.
• VB has been automatically declaring a default
  instance of Form1, the actual object that runs.

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Starting from Sub Main()

• Can manually declare the form object and launch
  it in code.
• Where? Add a code module to project with a Sub
  Main().
• Set the projects Startup Object to Sub Main().
  May need to uncheck App Framework!
• Sample Sub Main() Code Dim myform as New
  frmMain Myform.ShowDialog() lt- modal!

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Multiple Forms

• As app grows in complexity, one form may not be
  enough.
• Moving functionality to other helper forms
• Reduces clutter in main form
• Help user better focus on task at hand.
• Relationships between forms add complexity for
  programmer and user.
• We will see one model for keeping things simple.

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Modal vs Modeless Forms

• A modal form takes the applications focus until
  it is closed user cannot switch forms/windows.
• In VB launch modal form with .Show()
• A modeless form gets focus, but user can switch
  forms w/o closing it first.
• In VB launch modeless form with .Show()
• Modeless interface can be confusing without great
  care by programmer.

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Modal Form in MS Word

• User cannot work with document while Paragraph
  Format dialog box is onscreen.

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Modeless Form in MS Word

• User can work with document while Find dialog
  box is onscreen.
• Floating on top is not default behavior in VB.

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Designing a Custom Dialog Box

• Typical use some main form launches a helper
  form to obtain secondary (or more detailed) input
  from user.
• Reduces control clutter on main form.
• More flexible than just using InputBox or
  MessageBox can have any controls.
• Data is retrieved by main form from dialog.
• Dialog contains validation, type conversion or
  other pre-processing code.

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A Class Grade Averaging App

• Main form showsall students avgs and overall
  avg.
• Add Studentbutton opens dialog box.
• Dialog gets a students grades average.

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Behind the Scenes

• Code in Add Student button delcares the dialog
  form object (from frmStudent class)
• The dialog is dormant in memory, hidden and
  inactive.
• BUT its properties can be changed by code before
  being shown. Main form pushes data to dialog.
• Note dialog title (form Text) has been changed to
  show course no.

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Launching the Dialog Box

• studentForm.ShowDialog() will launch modally.
• User can still see main form, but cannot switch
  to it. Only closing the dialog will return
  focus.
• All application input goes to the dialog form.

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User Interaction w/Dialog

• Dialog form contians input validation code
• Other pre-processing?
• User cannot interact with main form until dialog
  is closed.

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Closing the Dialog

• User may want input used or discarded.
• Set form DialogResult property (OK/Cancel)in the
  relevant buttons event handler.
• Closing with upper right X button is Cancel.

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Dialog After Closing

• The original call to ShowDialog() returns the
  dialogs DialogResult value.
• Use the dialog data if not Canceled.
• Form is still in memory after closing.
• Main form pulls data from the dialog form.

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Simple Dialog Box Summary

• Main form creates instance of dialog form.
• Main form pushes to dormant dialog to pre-load
  data for editing or to change its properties.
• Launch modally with ShowDialog().
• User interacts with dialog, then closes it.
• If dialog not canceled, main form pulls data
  from dialog (now dormant again).
• Tip declare/push/show/close/pull.

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An Improvement

• Having the main form directly accessing dialog
  controls can be clumsy. Examples
• retrieving Text property of a TextBox to only to
  convert the string to a number
• checking Checked properties of a group of
  radiobuttons to map the input to a simple integer
  or character code. Male/female?
• Solution do this pre-processing work in the
  dialog form!
• Save the converted value to a public form-level
  variable in the dialog.
• Pull the already converted value from the form.

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Sample Main Form Button Code

• Private Sub btnStudent_Click(ByVal sender As
  System.Object, ByVal e As System.EventArgs)
  Handles btnStudent.Click, mnuAdd.Click create
  the dialog object
• Dim studentDlg As New frmStudentDlg
• 'PUSH data TO dialog to pre-load or
  customize
• studentDlg.Text "Student Grade Averager
  for " txtCourse.Text
• studentDlg.lblStudNum.Text "Student "
  _
  (lstStudAvgs.Items.Count
  1)
• 'show modally and check for canceled
  status upon closing
• If studentDlg.ShowDialog() ltgt
  DialogResult.Cancel Then
• OK to PULL data FROM dialog
  dblClassAvg ((dblClassAvg lstStudAvgs.Items.Co
  unt) _
  studentDlg.dblStudAvg) / (lstStudAvgs.Items.Count
  1)
• lstStudAvgs.Items.Add(FormatNumber(stu
  dentDlg.dblStudAvg, 2))
• txtClassAvg.Text FormatNumber(dblCla
  ssAvg, 2)
• End If
• End Sub

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Sample Dialog Button Code

• Private Sub btnSave_Click(ByVal sender As
  System.Object, ByVal e As System.EventArgs)
  Handles btnSave.Click
• input validation or data type
  conversion code here?
• Me.DialogResult DialogResult.OK
• End Sub
• Private Sub btnCancel_Click(ByVal sender As
  System.Object, ByVal e As System.EventArgs)
  Handles btnCancel.Click
• Me.DialogResult DialogResult.Cancel
• End Sub
• Doing the above immediately closes the form -- no
  call to Me.Close() is needed!

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Typical Dialog Properties

• FormBorderStyle FixedDialog
• ShowInTaskbar False
• MaximizeBox, MinimizeBox False
  inappropriate if opened modally!
• Dialog box forms do NOT have their own menus!

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Custom Modeless Forms

• Open with .Show()
• DialogResult is not relevant.
• A modeless interface easily gets confusing for
  user and programmer - - What do I do next? is
  often not clear.
• The simple declare/push/show/close/pull model
  breaks down.

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A Splash Screen

• Uses something for user to see while app loads,
  or useful in nagware demos.
• No buttons, closes automatically, quickly.
• Get splash screen to close itself
  MyBase.Close() on first Timer tick.
• Dont make main form (or user!) wait on splash
  form launch it modelessly with .Show() from main
  forms Load event.
• Set splashs TopMost True.

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Timer Control Specifics

• Timer is not a visible control.
• Shown in the Component Tray when added to form.
• Is disabled by default, must set EnabledTrue.
• Periodically fires the Tick event.
• Interval is in milliseconds (2000 2sec)